1. Field of the Invention
The present invention generally relates to head floating amount control methods and units, storage apparatuses and computer-readable programs, and more particularly to a head floating amount control method and a head floating amount control unit for controlling a floating amount of a head with respect to a recording medium, a storage apparatus which uses such a head floating amount control unit, and a computer-readable program which causes a computer to control the floating amount of the head by such a head floating amount control method. The present invention also relates to a computer-readable storage medium which stores such a computer-readable program.
2. Description of the Related Art
Storage apparatuses such as hard disk drives (HDDs) are used in various apparatuses such as desk-top personal computers, lap-top personal computers, servers, audio visual (AV) equipment, various kinds of portable electronic apparatuses including personal digital assistants (PDAs), and electronic apparatuses for automobiles including navigation apparatuses.
Due to the increase in the storage capacity of the HDDs, the recording density (surface density) of magnetic disks has increased, and the floating amount of the head with respect to the magnetic disk is becoming extremely small. In addition, in order to prevent damage to the head (or head crash) that is caused by head disk interference (HDI) generated due to the inconsistency or change in the head floating amount, improvements have been made to the head floating surface and the magnetic disk surface. The read performance, the write performance and the HDI reliability of the HDD are greatly affected by the change in the head floating amount, and a method has been proposed recently to control the head floating amount of the HDD by the HDD itself.
The floating amount of the head with respect to the magnetic disk accommodated within the HDD is controlled by a negative pressure generated between the head and the magnetic disk. The value of this negative pressure is approximately constant on an average depending on the shape of the head floating surface and the roughness of the magnetic disk surface, but is inconsistent among the individual heads and the corresponding magnetic disks. The effects of this inconsistency in the negative pressure on the read performance, the write performance and the margin until the head crash occurs are becoming larger as the recording density increases.
Accordingly, the floating amount of each of the heads within the HDD must be adjusted to a value such that the inconsistency among the floating amounts of the individual heads may be absorbed, and various proposals have been made to prevent the undesirable effects that are generated due to the change in the floating amount.
The floating characteristic of the conventional head is determined to fall within a range such that the inconsistency may be absorbed depending on the structure of the air bearing slider (ABS), the rotation windage loss at the radial position on the magnetic disk, the value of the negative pressure, the surface roughness of the magnetic disk and the like. For this reason, in a case where the inconsistency is large and particularly when the floating amount is small, the margin of the HDI with respect to the magnetic spacing deteriorates to thereby generate the possibility of the head crash.
On the other hand, when the floating amount is large, the efficiency of the electromagnetic conversion characteristic deteriorates due to the increase of the magnetic spacing. Consequently, there was a possibility of generating, to a certain extent, deterioration in the reproduced output, generation of the read error, and generation of the seek operation error caused by the read error with respect to the servo signal.
Furthermore, when the floating amount is small, there was a possibility of the head colliding with the projections on the surface of the magnetic disk. As a result, there was a possibility of generating the read error due to the thermal asperity or, causing damage to both the head and the magnetic disk due to the head colliding with the magnetic disk surface because of the repeated generation of the thermal asperity. Other than the thermal asperity, when the head floating surface makes contact with the magnetic disk surface, the lubricant coated on the magnetic disk surface may adhere to the head floating surface. In this case, the head crash may occur due to the change in the floating amount or the floating position of the head due to the damage caused by the contact between the head and the magnetic disk.
A method of controlling the thermal protrusion of the head floating surface with respect to the magnetic disk is proposed in a Japanese Laid-Open Patent Application No. 2005-71546, for example. A method of suppressing the thermal asperity by removing the projections on the magnetic disk surface is proposed in a Japanese Laid-Open Patent Application No. 10-241333, for example. Methods of controlling the floating amount of the head with respect to the disk by controlling heat generated by a heater that is built into the head are proposed in Japanese Laid-Open Patent Applications No. 2003-168274, No. 2003-272335, No. 2006-4474 and No. 2006-18987, for example. A method of detecting the thermal asperity is proposed in a Japanese Laid-Open Patent Application No. 11-185210, for example.
Therefore, conventionally, particularly when the inconsistency among the floating amounts of the individual heads is large, the margin with respect to the magnetic spacing of the HDI deteriorates if the floating amount is small, and there was a possibility of generating the head crash. In addition, if the floating amount is small, there was a possibility of the head colliding with the projections on the magnetic disk surface, to thereby generate the read error due to the thermal asperity or, to damage both the head and the magnetic disk due to the head colliding with the magnetic disk surface because of the repeated thermal asperity. In addition, when the head floating surface and the magnetic disk make contact, the lubricant coated on the magnetic disk surface may adhere to the head floating surface, and the head crash may occur due to the change in the floating amount or the floating position of the head due to the damage caused by the contact between the head and the magnetic disk.
On the other hand, if the floating amount is large, the efficiency of the electromagnetic conversion characteristic deteriorates due to the increase of the magnetic spacing, and there was a possibility of deteriorating the reproduced output, generating the read error, and generating the seek operation error caused by the read error with respect to the servo signal.
In other words, if the floating amount is set relatively small in order to improve the efficiency of the electromagnetic conversion characteristic, there was a possibility of generating the head crash particularly when the inconsistency among the floating amounts of the individual heads is large, and if the floating amount is set relatively large in order to prevent the head crash, the efficiency of the electromagnetic conversion characteristic deteriorated particularly when the inconsistency among the floating amounts of the individual heads is large.